1. Field of the Invention
The present invention relates to a novel organic compound and an electrochromic element having the same.
2. Description of the Related Art
As electrochromic (hereinafter abbreviated to as “EC” in some cases) materials, the optical absorption properties (colored state, light transmittance, and the like) of which are changed by an electrochemical oxidation-reduction reaction, various materials have been reported. As inorganic EC materials, a compound using a metal oxide, such as WO3, has been known.
As organic EC materials, for example, a conductive polymer used in an EC element described in Japanese Patent Laid-Open No. 56-67881 and an EC material using an organic low molecular weight compound, such as an oligothiophene, disclosed in M. G. Hill, J. F. Penneau, B. Zinger, K. R. Mann, L. L. Miller, Chemistry of Materials, 4 (1992) 1106 have been known.
When the conductive polymer described in Japanese Patent Laid-Open No. 56-67881 is electrochemically oxidized or reduced, the π-conjugated chain length of its main chain is changed, and as a result, the absorption wavelength is changed.
When being in a neutral state, these conductive polymers have absorption in the visible light region and hence are colored, and when the polymers are in an oxidized state, the absorption wavelength shifts to a long wavelength side (infrared region side). That is, the absorption is no longer present in the visible light region, and as a result, the EC element loses its color.
In addition, in the oligothiophene compounds described in Chemistry of Materials, 4 (1992) 1106, it has been disclosed that when an oligothiophene derivative is oxidized or reduced in a solution, the absorption wavelength thereof is changed and that when a terminal group of the oligothiophene derivative is blocked by a substituent group, its oxidative polymerization can be suppressed.
According to Japanese Patent Laid-Open No. 56-67881, unstable radical cations are delocalized in the molecule to enhance the stability thereof. However, the stability is not sufficient, and when oxidation and reduction reactions are repeatedly performed, the material is deteriorated, and as a result, the performance thereof is also disadvantageously degraded.
In addition, when being in a neutral state, this conductive polymer has an absorption band in the visible light region. Hence, at portions at which an electrochemical reaction insufficiently occurs, the colored state still slightly remains, and hence high transparency is difficult to achieve.
In Chemistry of Materials, 4 (1992) 1106, aromatic compounds, such as an oligothiophene compound, having π electrons have been disclosed.
Products formed by oxidation of the disclosed aromatic compounds are in an equilibrium state between radical cation monomers and dimers (π-dimers) generated by their overlapped π electron clouds.
The absorption wavelength of the π-dimer is different from that of the radical cation monomer. Furthermore, the abundance ratio between the π-dimers and the radical cation monomers has the temperature dependence.
Since the light absorption wavelength and the light absorption intensity in the colored state have the temperature dependence, when an EC element is used as a device, the color thereof is disadvantageously changed by the change in temperature.